80 
MR. HARRIS ON THE TRANSIENT MAGNETIC STATE 
measure on the mass, it seemed of consequence to ascertain how far the energy 
might vary with the density. Several kinds of wood therefore of the above 
dimensions were subjected to experiment, whose specific gravities greatly 
varied; but there did not appear, after many trials, any perceptible difference 
on 280 vibrations. The woods tried were, Lignum Vitse, Yellow Pine, African 
Oak, Honduras Mahogany, and Teak. All these reduced the vibrations of 
the bar from 420, the number performed in free space, to 280, the number 
performed when surrounded by the wood ; the vibrations being taken from 
45° to 10°, in an exhausted receiver. 
20. I endeavoured to detect the magnetic energy of fluid bodies by vibrating 
the bar in an exhausted receiver, with its poles within the T vth 0 f an inch of 
the glass ; the receiver being surrounded at that part opposite the pole of the 
magnet by the particular fluid, the subject of experiment. In this case the 
fluid was retained in its situation by means of an external check of glass ground 
to a glass-plate, on which the whole was sustained ; the plate being supported 
on a ring of glass placed over and in connection with the pump-plate below ; 
and the surfaces of contact ground, so as to fit air-tight. I failed however 
in arriving at any decided result ; the amount of the retardation with sul- 
phuric acid, for example, not appearing greater than was fairly attributable to 
the influence of the glass alone : even a saturated solution of sulphate of iron 
did not seem to exert in this way any sensible influence. By means of a very 
great number of vibrations, and a powerful bar, however, the energy of fluids, 
if such exist, might possibly become appreciable. 
21. The inductive influence on metallic bodies being the most decisive, 
they are perhaps better adapted to the purposes of experiments relating to the 
influence of mass and density, or to the law according to which the inductive 
effect increases, as the distance from the magnet decreases, than any other 
kind of substance. Before examining, therefore, the comparative energies of 
various metals, I endeavoured to arrive at some further conclusions in this 
interesting part of the inquiry. In order to examine the comparative energies 
when the quantity of matter was varied, twelve concentric rings of copper 
were employed similar to the former ring of wood (17), except in thickness, 
which amounted to .025 of an inch : these rings were turned up with suffi- 
cient accuracy, and fitted very fair and close one within the other. The num- 
